Electrode unit, electrolytic cell comprising electrode unit and electrolytic device

ABSTRACT

According to one embodiment, an electrode unit of an electrolytic device includes a first electrode including a first surface, a second surface located on an opposite side to the first surface, a plurality of first pores opened in the first surface, a plurality of second pores opened in the second surface and having an opening area greater than that of the first pores, and a plurality of the first pores communicating with a respective one of the second pores, a second electrode opposing the first surface of the first electrode, and a continuous porous membrane arranged between the first electrode and the second electrode, so as to cover the first surface of the first electrode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of PCT Application No.PCT/JP2015/056547, filed Mar. 5, 2015 and based upon and claiming thebenefit of priority from Japanese Patent Application No. 2014-192015,filed Sep. 19, 2014, the entire contents of all of which areincorporated herein by reference.

FIELD

Embodiments described herein relate generally to an electrode unit, anelectrolytic cell comprising the electrode unit and an electrolyticdevice.

BACKGROUND

In recent years, an electrolytic device for electrolyzing water andproducing electrolyzed water which has various functions, such asionized alkaline water, ozone water or aqueous hypochlorous acid hasbeen provided. Of the electrolyzed water, aqueous hypochlorous acid hasexcellent sterilizing power and also is safe to human health; thereforeit has been approved as a food additive.

As an electrolytic device, an electrolyzed-water production devicecomprising, for example, a three-chamber electrolytic cell is proposed.The inside of the electrolytic cell is divided into three chambers,namely, an intermediate chamber, and also an anode chamber and a cathodechamber located on both side of the intermediate chamber. The anodechamber and the cathode chamber are provided with an anode and acathode, respectively. As the electrodes, a porous-structure type isemployed, in which a great number of pores are made by processing suchas expanding, etching or punching in a metal plate matrix.

In this type of electrolytic device, for example, salt water is suppliedto the intermediate chamber, and water is supplied to the anode andcathode chambers. The salt water in the intermediate chamber iselectrolyzed by the cathode and the anode. In this manner, aqueoushypochlorous acid is produced from gaseous chlorine produced by theanode. Aqueous sodium hydroxide is produced in the cathode chamber. Theproduced hypochlorous acid is used as sterilizing water. The aqueoussodium hydroxide is used as a cleaning solution.

In the three-chamber electrolytic cell, the anion-exchange membrane isdegraded easily by chlorine or hypochlorous acid. When the electrodehaving a porous configuration adheres tightly to the ion-exchangemembrane (electrolyte membrane), stress is easily concentrated on theedge portion of the pores of the electrode. Thus, the diaphragm formedof, for example, a thin electrolyte membrane which is weak mechanically,is deteriorated easily. In consideration of this factor, the followingtechnique is suggested. To reduce the degradation of the electrode bychlorine, nonwoven fabric having overlaps or slits is inserted betweenthe electrode having a porous configuration and the electrolytemembrane.

However, if a porous membrane such as nonwoven fabric is insertedbetween the electrode and the electrolytic membrane, stress is appliedto the porous membrane, causing variation in thickness in the porousmembrane. In other words, the thickness of the porous membrane becomesuneven. The porous membrane of an uneven thickness causes irregularelectrolytic reaction, resulting in reduction of the reactivity of theelectrolytic device or degradation of the electrolytic membrane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an electrolytic device according to afirst embodiment.

FIG. 2 is a sectional view showing an electrode unit of the electrolyticdevice according to the first embodiment.

FIG. 3 is an exploded perspective view of the electrode unit.

FIG. 4 is a sectional view showing a manufacturing process of anelectrode.

FIG. 5 is a sectional view of an electrolytic device according to asecond embodiment.

FIG. 6 is a perspective view of the electrode unit according to thesecond embodiment.

FIG. 7 is a sectional view of an electrode unit of an electrolyticdevice according to a third embodiment.

FIG. 8 is a perspective view of an electrode unit according to a fourthembodiment.

FIG. 9 is a sectional view of an electrolytic device according to afifth embodiment.

FIG. 10 is a sectional view of an electrolytic device according to asixth embodiment.

FIG. 11 is a sectional view of an electrode unit according to the thirdembodiment.

FIG. 12 is a perspective view of a first electrode and a secondelectrode according to a modification.

FIG. 13 is a sectional view schematically showing a porous membranecontaining inorganic oxide and including pores formed in a planarly orthree-dimensionally irregular manner.

FIG. 14 is a sectional view schematically showing a porous membraneconsisting of a multi-layered film.

DETAILED DESCRIPTION

Various embodiments will be described in detail with reference todrawings. In general, according to one embodiment, an electrolyticdevice comprises an electrode unit. The electrode unit comprises: afirst electrode including a first surface; a second surface located onan opposite side to the first surface, a plurality of first pores openedin the first surface, a plurality of second pores opened in the secondsurface and having an opening area greater than that of the first pores,and a plurality of first pores communicating with a respective one ofthe second pores; a second electrode opposing the first surface of thefirst electrode; and a continuous porous membrane interposed between thefirst electrode and the second electrode, so as to cover the firstsurface of the first electrode.

Throughout the embodiments, common structural members are designated bythe same reference symbols, and the explanation thereof will not berepeated. Further, the drawings are schematic diagrams designed toassist the reader to understand the embodiments easily. Thus, there maybe sections where the shape, dimensions, ratio, etc. are different fromthose of the actual devices, but they can be re-designed as needed withreference to the following explanations and publicly known techniques.For example, the electrodes are illustrated in plane in these figures,but they may be curved or formed in cylindrical according to the shapeof the respective electrode units.

First Embodiment

FIG. 1 is a diagram briefly showing an electrolytic device according tothe first embodiment. The electrolytic device 10 comprises, for example,a two-chamber electrolytic cell 11, and an electrode unit 12 provided inthe electrolytic cell 11. The electrolytic cell 11 is formed into a flatrectangular box, the inside of which is divided by an electrode unitinto two compartments, namely, an anode chamber 16 and a cathode chamber18 by a dividing wall 14 and electrode unit 12.

The electrode unit 12 comprises a first electrode (anode) 20 located inthe anode chamber 16, a second electrode (a counterelectrode or acathode) 22 located in the cathode chamber 18, and a porous membrane 24and a diaphragm provided between the first and second electrodes.

The electrolytic device 10 comprises a power supply 30 to drive thefirst and second electrodes 20 and 22 of the electrode unit 12, anammeter 32, a voltmeter 34 and a control device 36 that controls themembers. A flow channel for liquid may be provided in the anode chamber16 and the cathode chamber 18. For example, a pipe or a pump forsupplying liquid from outside or discharging liquid may be connected tothe anode chamber 16 and the cathode chamber 18. A porous spacer may beprovided between the electrode unit 12 and the anode chamber 16 or thecathode chamber 18.

Next, the electrode unit 12 will be described in detail. FIG. 2 is asectional view of the electrode unit. FIG. 3 is an exploded perspectiveview of the electrode unit.

As shown in FIGS. 2 and 3, the first electrode 20 has a porous structurein which numerous through-holes are formed in a matrix 21 of, forexample, a rectangular metal plate. The matrix 21 includes a firstsurface 21 a and a second surface 21 b opposing and substantiallyparallel to the first surface 21 a. The interval between the firstsurface 21 a and the second surface 21 b, in other words, the thicknessof the matrix 21, is defined as T1. The first surface 21 a opposes theporous membrane 24 and the second surface 21 b opposes the anode chamber16.

A plurality of first pores 40 of, for example, a square shape, areformed in the first surface 22 a of the matrix 21 to open on the firstsurface 22 a. Moreover, a plurality of second pores 42 are formed in thesecond surface 22 b to open on the second surface 22 b. The opening areaof the second pores 42 is greater than that of the first pores 40. Thefirst pores 40 made on the porous membrane 24 side, have a dimension R1of the opening, which is less than a dimension R2 of the openings of thesecond pores 42 of, for example, a square shape. Further, the firstpores 40 are more in number than the second pores 42. The depth of thefirst pores 40 is T2 and the depth of the second pores 42 is T3, andT2+T3=T1. In this embodiment, the holes are made such that T2<T3.

In this embodiment, the second pores 42 are formed into, for example, asquare shape to be arranged in a matrix on the second surface 22 b. Thecircumferential wall which defines each second pore 42 may be formed tohave a tapered surface 42 a or curved surface so that the hole enlargestoward the second surface 22 b side from the bottom of the hole to theopening. The interval between adjacent second pores 42, that is, thewidth of a linear portion 60 a of the electrode is set to W2. Note thatthe second pores 42 are not limited to a rectangular shape, but may takevarious other forms. Moreover, the second pores 42 may not necessarilybe arranged regularly, but may be at random.

The opening diameter of the first pores 40 is preferably less in orderto make the pressure uniform. However, the first pores 40 need to belarge to the extent that substance diffusion can be prevented. In caseof a square, the length of each side of the opening is preferably 0.1 to2 mm, and is more preferably 0.3 to 1 mm. The opening may take a varietyof forms such as a square, a rectangle, a rhomboid, a circle and anellipse, and the vertices of a square, a rectangle or a rhomboid may berounded. The opening area is preferably 0.01 to 4 mm² in the same manneras the above-described square. The opening area is more preferably 0.1to 1.5 mm². The opening area is further preferably 0.2 to 1 mm². Theratio of the opening area to the electrode area including the opening(in other words, the opening ratio) is preferably 0.05 to 0.5, and ismore preferably 0.1 to 0.4, and is further preferably 0.15 to 0.3. Ifthe opening ratio is excessively less, outgassing is difficult. If theopening ratio is excessively great, electrode reaction is inhibited.

The first pores 40 are formed into, for example, a square shape and arearranged in a matrix on the first surface 21 a. The circumferential wallwhich defines each first pore 40 may be formed to have a tapered surface40 a or curved surface so that the dimension enlarges from the bottom ofthe hole to the opening, in other words, to the first surface 22 a. Inthis embodiment, a plurality, for example, nine of first pores 40 opposea respective second pore 42 and communicate therewith to be made all theway through the matrix 21. An interval W1 between adjacent first pores40 is set so as to be less than an interval W2 between second pores 42.With this structure, the number density of the first pores 40 in thefirst surface 21 a is sufficiently greater than that of the second pores42 in the second surface 21 b.

Various shapes may be employed for each second pore 42, such as asquare, a rectangle, a rhomboid, a circle or an ellipse. The openingdimension of each second pore 42 is preferably great in order tofacilitate outgassing. However, if the opening dimension is great, theelectrical resistance is increased. Therefore, the second pores 42cannot be significantly enlarged. In the case of the square opening, oneside is preferably 1 to 40 mm, more preferably 2 to 30 mm, and furtherpreferably 3 to 20 mm. The opening may take a variety of forms such as asquare, a rectangle, a rhomboid, a circle and an ellipse, while theopening area is preferably 1 to 1600 mm² in the same manner as theabove-described square. The opening area of the second pores 42 is morepreferably 4 to 900 mm², and is further preferably 9 to 400 mm². Forexample, the opening may be shaped as a rectangle or an ellipse which islong in one direction so as to connect an end and the other end of theelectrode.

For the matrix 21 of the first electrode 20, a valve metal such astitanium, chromium or aluminum, or an alloy of these, or a conductivemetal can be used. Out of these materials, titanium is preferable. Itmay be desirable, depending on the electrolytic reaction, to form anelectrolytic catalyst (catalyst layer) on the first surface and thesecond surface of the electrode. When used as an anode, it is desirableto use a precious metal catalyst such as platinum or an oxide catalystsuch as iridium oxide, as the matrix itself of the electrode. The amountof electrocatalyst per unit area on one surface of the electrode maydiffer from that on the other surface thereof. In this manner, forexample, a side reaction may be prevented.

Further, the first pores 40 may not necessarily be arranged regularly,but may be at random. Furthermore, all the first pores 40 may notnecessarily communicate with the second pores 42, but there may be somefirst pores not communicating with a second pore 42. Thus, some firstpores 40 may not communicate with the anode chamber 16. For example, asshown in FIG. 12, the first pores 40 and 44 may be rectangles extendingfrom near one end of the electrode to near the other end, within which aplurality of openings 41 a and 45 a communicating with the second pores42 and 46 are arranged at certain interval. Only some of the first pores40 and 44 may communicate with the second pores 42 and 44. The firstpores 40 and 44 which do not communicate with the second pores 42 and 44can increase the electrode area.

Preferably, 85% or more of all of the first pores 40 and 44 have anopening area of 0.01 to 4 mm². More preferably, 90% or more, and furtherpreferably, 95% or more of all of the first pores 40 have an openingarea of 0.01 to 4 mm².

The first electrode 20 can be manufactured by, for example, an etchingmethod using a mask. FIG. 4 briefly shows the manufacturing methodthereof. As shown in FIGS. 4(a) and (b), one flat matrix 21 is prepared.Resist films 50 a and 50 b are applied to the first and second surfaces22 a and 22 b of the matrix 21. Then, as shown in FIG. 4(c), the resistfilms 50 a and 50 b are exposed using an optical mask (not shown) andthus etching masks 52 a and 52 b are formed, respectively. As shown inFIG. 4(d), wet etching is applied to the first and second surfaces 22 aand 22 b of the matrix 21 via the masks 52 a and 52 b with solution. Inthis manner, a plurality of first pores 40 and a plurality of secondpores 42 are formed. Subsequently, the first electrode 20 is obtained byremoving the masks 52 a and 52 b.

The shape of the tapered or curved surface of the first and second pores40 and 42 can be controlled based on the material of the matrix 21 andetching conditions. The depth of the first pores 40 is T2, and the depthof the second pores 42 is T3. As stated above, the first and secondpores are formed such that T2<T3. In etching, both surfaces of thematrix 21 may be etched at the same time, or may be etched separately.The type of etching is not limited to wet etching. For example, dryetching may be employed. Moreover, not only etching but also processingby laser, precision cutting or the like may be employed to manufacturethe first electrode 20.

As shown in FIGS. 1 to 3, in this embodiment, the second electrode(counterelectrode) 22 is structured in the same manner as the firstelectrode 20. More specifically, the second electrode 22 has a porousconfiguration in which a large number of through-holes are formed in amatrix 23 made of, for example, a rectangular metal plate. The matrix 23includes a first surface 23 a and a second surface 23 b opposing andsubstantially parallel to the first surface 23 a. The first surface 23 aoppose a diaphragm 26. The second surface 23 b opposes the cathodechamber 18.

A plurality of first pores 44 are formed in the first surface 23 a ofthe matrix 23 to open on the first surface 23 a. Further, a plurality ofsecond pores 46 are formed in the second surface 23 b to open on thesecond surface 23 b. The opening area of the first pores 42 on thediaphragm 26 is less than that of the second pores 44. Further, thefirst pores 44 are more in number than the second pores 46. The depth ofthe first pores 44 is less than that of the second pores 46.

A plurality, for example, nine of first pores 44 are provided to opposeone second pore 46. Each of these first pores 44 communicates with thesecond pore 26 so as to be made through the matrix 23. The intervalbetween adjacent first pores 44 is set so as to be less than theinterval between the second pores 46. With this structure, the numberdensity of the first pores 44 on the first surface 23 a is sufficientlygreater than that of the second pores 46 on the second surface 23 b.

The porous membrane 24 and the diaphragm 26 are interposed between thefirst surface 22 a of the first electrode 20 and the first surface 23 aof the second electrode 22. The continuous porous membrane 24 is formedin, for example, a rectangular shape so as to have dimensionssubstantially equal to those of the first electrode 20, and opposes thewhole first surface 21 a. As the porous membrane 24, for example, anonwoven fabric, cloth or a porous membrane which is formed by a sol-gelmethod can be used, and various materials may be used for the porousmembrane. The porous membrane needs to be chemically stable. Inparticular, it needs stability to, especially, chlorine, hypochlorousacid or oxygen, or resistance to acid or alkali. Further, when used toprocess foods, for example, the following requirements should be met.That is, when it is a polymer, monomers or the like must not dissolve atamount determined by the law or more, or when it is an inorganicmaterial, heavy metal ion must not dissolve at amount determined by thelaw or more. Mechanically, when the porous membrane is solely usedwithout an undercoat member, it is important for the membrane to behandled easily, and therefore the thickness thereof is preferably 20 to500 μm. If the porous membrane is formed directly on an electrode, itmay be thin, but in order for the membrane to exhibit its properties,the thickness is preferably 50 nm or greater. Of these porous membranes,a polymer membrane containing a fluorine atom or a chlorine atom in itsmain chain, glass cloth or a membrane including irregular continuouspores and containing inorganic oxide, is especially chemically stableand preferable. As the polymer membrane, Teflon is particularlypreferable. Hydroxide, alkoxide, oxyhalide or hydrate may be containedin the inorganic oxide. When the inorganic oxide is prepared by thehydrolysis of metal halide or metal alkoxide, a composite thereof may beeasily obtained though it depends on the temperature of the subsequenttreatment. The polymer membrane, glass cloth and inorganic oxide may becombined, and for example, the polymer membrane and glass cloth may becovered by an inorganic oxide. As shown in FIG. 13, if an inorganicoxide film having irregular pores in a plane or in a three-dimensionalmanner is used as the porous membrane 24, it may also function as adiaphragm. In other words, the diaphragm 26 may be omitted.

As shown in FIG. 14, for the porous membrane 24, a multilayer filmincluding a plurality of porous membranes 27 a and 27 b having differentpore diameters may be used. In this case, if the pore dimension of theporous membrane 27 b located on the diaphragm 26 side is set greaterthan that of the porous membrane 27 b located on the first electrode 20side, migration of ions is more facilitated, and the stressconcentration due to the pores of the electrode can be reduced. This isbecause as the opening on the diaphragm 26 side is greater, the ionmigration by diffusion becomes easier. When the first electrode 20 isused for the anode, a positive potential is applied. Therefore, even ifthe pore diameter on the first electrode 20 side is less, anions areeasily attracted to the first electrode 20. If the pore diameter on theelectrode 20 side is great, the produced chlorine or like is easilydiffused to the porous membrane 24 side.

The pore diameter on the surface of the porous membrane 24 can bemeasured by a high-resolution scanning electron microscope (SEM). Thepores inside the porous membrane can be measured by cross-sectional SEMobservation.

As shown in FIGS. 2 and 3, the diaphragm 26 is formed into, for example,a rectangular shape with dimensions substantially equal to those of thefirst electrode 20, and also provided between the first surface 23 a ofthe electrode 22 and the porous membrane 24. The diaphragm 26 is tightlyattached to the entire first surface 23 a of the second electrode 22,and further to the porous membrane 24.

The diaphragm 26 located between the first and second electrodes 20 and22 is a film which allows ions and/or liquid to pass therethrough. Forthe diaphragm 26, various electrolyte membranes and porous membraneshaving nanopores may be used. For the electrolyte membrane, a polymerelectrolyte membrane, for example, a cation-exchange solid polymerelectrolyte membrane, more specicially, a cation-exchange membrane, ananion-exchange membrane or a hydrocarbon-based film may be used.Examples of the cation-exchange membrane are NAFION 112, 115 and 117(trademark of E. I. du Pont de Nemours & Co.), Flemion (trademark ofAsahi Glass Co., Ltd.), ACIPLEX (trademark of Asahi Chemical Co., Ltd.)and GOA SELECT (trademark of W. L. Goa and associates co.). An exampleof the anion-exchange membrane is A201 of Tokuyama, Inc. Usable examplesof the porous membranes having nanopores are porous ceramics such asporous glass, porous alumina, porous titania and porous zeolite, andporous polymers such as porous polyethylen, porous propylene, porousteflon and porous polyimide.

The first electrode 20, the porous membrane 24 and the second electrode22 having the above-described structures are brought into contact witheach other by pressing them in a state where the porous membrane 24 isinterposed between the first electrode 20 and the second electrode 22.In this manner, the electrode unit 12 is obtained.

As shown in FIG. 1, the electrode unit 12 is provided in theelectrolytic cell 11 and is attached to the dividing wall 14. Theelectrolytic cell 11 is divided into the anode chamber 16 and thecathode chamber 18 by the dividing wall 14 and the electrode unit 12.Thus, the electrode unit 12 is disposed in the electrolytic cell 11 sothat the direction where the components which constitute this are incontact with each other is, for example, horizontal. The first electrode20 of the electrode unit 12 faces the anode chamber 16. The secondelectrode 22 faces the cathode chamber 18.

In the electrolytic device 10, both poles of the power supply 30 areelectrically connected to the first electrode 20 and the secondelectrode 22. The power supply 30 applies a voltage to the electrodeunit 12 under the control of the control device 36. The voltmeter 34 iselectrically connected to the first electrode 20 and the secondelectrode 22 and detects the voltage applied to the electrode unit 12.The detection data is supplied to the control device 36. The ammeter 32is connected to the voltage application circuit of the electrode unit 12and detects the current flowing in the electrode unit 12. The detectiondata is supplied to the control device 36. The control device 36controls the application of voltage or load for the electrode unit 12 bythe power supply 30 based on the detected data in accordance with theprogram stored in the memory. The electrolytic device 10 applies avoltage or load between the first electrode 20 and the second electrode22 in a state where the substance for reaction is supplied to the anodechamber 16 and the cathode chamber 18. In this manner, theelectrochemical reaction for electrolysis is advanced. The electrolyticdevice 10 of the present embodiment should preferably electrolyze anelectrolyte containing chloride ions.

According to the electrolytic device and the electrode unit having theabove-described structure, in the first electrode 20, the diameter(opening area) of the first pores 40 formed in the first surface 22 a onthe porous membrane 24 side is made less than that of the second pores42. Thus, the number density thereof is increased. This structure allowsthe reduction in the concentration of stress applied from the firstelectrode 20 side to the porous membrane 24. As a continuous membrane,the porous membrane 24 is brought into contact with the whole firstsurface 21 a of the first electrode 20. Thus, the holes of the firstelectrode 20 are covered by the porous membrane 24. The distance betweenthe first electrode 20 and the diaphragm 26 can be easily maintainedequally over the whole surface. That is, distribution in the thicknessof the porous membrane 24 can be prevented and it becomes possible tomaintain the thickness of the porous membrane 24 uniformly. Thisstructure enables the electrolytic reaction to occur uniformly, therebyimproving the reaction efficiency of the electrolytic device andpreventing the degradation of the electrolyte membrane.

Further, the first electrode 20 is formed to have the first pores 40with a tapered or curved shape which enlarges towards the first surfaceside of the electrode. With this structure, the contact angle betweenthe first pores 40 and the porous membrane 24 is obtuse, thereby makingit possible to further reduce the concentration of stress on the porousmembrane 24 from the first electrode 20 side. Note that the firstsurface 22 a on the porous membrane 24 side of the first electrode 20 ispreferably substantially flat except for recess portions. The recessportions may be the first pores described above or recessed sectionswhich will be described later.

When the opening area of the second pores 42 formed in the secondsurface 22 b of the first electrode 20 is increased and the numberdensity is reduced, width W2 of the linear portions between the secondpores 42 can be made sufficiently great. Thus, the mechanical strengthof the first electrode 20 can be maintained high and the electricresistance can be reduced.

In the first embodiment having the above-described structures, it ispossible to obtain a long-life, high-reaction-efficiency electrode unitand electrolytic device.

Note that in the first embodiment, the second electrode 22 has a porousstructure with the first and second pores with different diameters, butit is not limited to this. For example, a plate electrode without athrough-hole may be employed. Or such an electrode may be employed aswell, that an electrode substrate is processed to have through-holes ofthe same diameter on the first surface and the second surface. Thesecond electrode 22 and the diaphragm 26 may be in contact with eachother, or a separate structural member may be interposed therebetween.

Next, an electrolytic cell and an electrolytic device according toanother embodiment will be described. Note that in the other embodimentsdescribed below, the same reference symbols are given to the samestructural elements as the first embodiment above, and the detailedexplanations thereof are omitted. The portions different from those ofthe first embodiment will be mainly discussed.

Second Embodiment

FIG. 5 is a sectional view showing an electrode unit of an electrolyticdevice according to the second embodiment and FIG. 6 is a perspectiveview of an electrode.

According to the second embodiment, in the electrode unit 12, the firstsurface 22 a of the first electrode 20 is formed flat, and the firstpores 40 described above are formed in the first surface 22 a so as tobe made through the matrix 21. A plurality of recess portions 54 areformed in the first surface 22 a of the first electrode 20. In otherwords, the first electrode 20 includes recess portions 54, which arerecesses which are not made through the matrix 21. The recess portions54 are formed from, for example, continuous grooves extending betweenthe first pores 40. Or the recess portions 54 may be a great number ofindependent dot-like recesses.

The porous membrane 24 is tightly attached to the first surface 22 a ofthe first electrode 20 and further opposes the first pores 40 and recessportions 54 to stop them.

The first surface 22 a of the first electrode 20 is preferably flatexcept for the first pores 40 and the recess portions 54. With therecess portions 54, the electrode area can be increased, and also, flowchannels for extracting the produced gas can be created. By forming thefirst surface 22 a of the first electrode 20 substantially plate-likeexcept for the recess portions 54, the concentration of the stress onthe porous membrane 24 can be further reduced. Although it varydepending on the thickness of the porous membrane 24, the flatness ofthe first surface 22 a, or the average surface roughness, is preferably10% or less of the average thickness of the porous membrane 24, morepreferably, 5% or less, or further preferably, 2% or less. The averagesurface roughness can be examined by cross-sectional SEM observation.

Note that not only the first electrode 20, but also the first surface 23a of the second electrode 22 may be provided with a plurality of recessportions.

Third Embodiment

FIG. 7 is a sectional view showing an electrode unit of an electrolyticdevice according to the third embodiment. According to the thirdembodiment, an electrically insulating film 56 which does not allowliquid to pass, is formed on at least a portion of the surface of thefirst electrode 20. In the first electrode 20, gas such as chlorineproduced by the reaction is not easily discharged on the first surface22 a, which is widely in contact with the porous membrane 24 on thediaphragm 26 side. For this reason, the diaphragm 26 is deterioratedeasily by the produced gas. Here, by covering the region of the firstsurface 22 a where the first pores 40 are not formed with the insulatingfilm 56, the production of the reactive gas is suppressed in thisregion, and thus the deterioration of the diaphragm 26 can be prevented.In this embodiment, the insulating film 56 is formed on both thesurfaces of the broad linear portion (width W2) of the first electrode20.

However, the reactive area of the first electrode 20 decreases byforming the insulating film 56. Therefore, it is desirable to have thereaction of the first electrode 20 occur sufficiently in the portionwhere the produced gas can easily escape. Further, an electricallyinsulating film 57 may be formed for cover on the second surface 22 b ofthe first electrode 20 located on the opposite side to the diaphragm 26.When such an electrode unit 12 is used for a three-chamber electrolyticcell, a side reaction on the second surface 22 b side can be reduced.Note that a portion of the insulating film may protrude in the sectionaldirection of the electrode.

Fourth Embodiment

FIG. 8 is a perspective view showing an electrode unit of anelectrolytic device according to the fourth embodiment. According to thefourth embodiment, an interval W3 between adjacent first pores 40 formedin the central portion of the electrode is set to be greater than aninterval W1 between those formed in the peripheral portion of theelectrode. With this structure, the opening ratio (the ratio of theopening area to the electrode area including the opening area) of thecentral portion of the first electrode 20 is smaller than that of theperipheral portion of the first electrode 20. Therefore, the electricresistance can be made lower in the central portion of the firstelectrode 20 than in the peripheral portion, thereby making it possibleto reduce the voltage rise in the central portion of the electrode evenin the case where power is supplied from the periphery of the electrodeto the electrode. In order to reduce the opening ration, the openingarea of the first pores 40 formed in the central portion of the firstelectrode 20 can be reduced by reducing the open area of those formed inthe periphery as shown in FIG. 8, or the number of pores can be reducedin the central portion.

Fifth Embodiment

FIG. 9 is a sectional view showing an electrolytic device according tothe fifth embodiment. In the fifth embodiment, an electrolytic cell 11of an electrolytic device 10 is structured as a one-chamber electrolyticcell comprising only one electrolytic chamber 17. An electrode unit 12is provided in the electrolytic chamber 17. For example, a pipe or apump for supplying an electrolyte from outside or discharging anelectrolyte may be connected to the electrolytic chamber 17.

In the one-chamber electrolytic cell 11, a second electrode(counterelectrode) 22 of the electrode unit 12 preferably has a porousconfiguration in a manner similar to that of the first electrode 20. Theporous configuration enables the electrode area to be increased.

Sixth Embodiment

FIG. 10 is a sectional view showing an electrolytic device according tothe sixth embodiment and FIG. 11 is a sectional view of an electrodeunit in the electrolytic device.

As shown in FIG. 10, an electrolytic device 10 comprises a three-chamberelectrolytic cell 11 including an electrode unit 12. The electrolyticcell 11 is formed into a flat rectangular box shape, the inside of whichis divided into three chambers, specifically, an anode chamber 16, acathode chamber 18 and an intermediate chamber 19 formed between theelectrodes, by a dividing wall 14 and the electrode unit 12.

The electrode unit 12 comprises a first electrode (anode) 20 disposed inthe anode chamber 16, a second electrode (counterelectrode or cathode)22 disposed in the cathode chamber 18, two diaphragms 26 a and 26 bprovided between the first and second electrodes, a porous membrane 24 ainterposed between the first electrode 20 and the diaphragm 26 a, and aporous membrane 24 b interposed between the second electrode 22 and thediaphragm 26 b. The diaphragms 26 a and 26 b oppose each other with anintervening space such that they are parallel to each other. Theintermediate chamber (electrolyte chamber) 19 which holds an electrolyteis formed between the diaphragms 26 a and 26 b. A holder 25 which holdsan electrolyte may be provided in the intermediate chamber 19. The firstand second electrodes 20 and 22 may be connected to each other by aplurality of insulating bridges 60.

The electrolytic device 10 comprises a power supply 30 which applies avoltage to the first and second electrodes 20 and 22 of the electrodeunit 12, an ammeter 32, a voltmeter 34 and a control device 36 whichcontrols these elements. A flow channel for liquid may be provided inthe anode chamber 16 and the cathode chamber 18. For example, a pipe ora pump for supplying liquid from outside or discharging liquid may beconnected to the anode chamber 16 and the cathode chamber 18. A porousspacer may be provided between the electrode unit 12 and the anodechamber 16 or the cathode chamber 18 depending on the case.

As shown in FIGS. 10 and 11, in the electrode unit 12, the first andsecond electrodes 20 and 22 are formed to have a porous configurationsimilar to that of the first embodiment discussed above. The continuousporous membrane 24 is formed in, for example, a rectangular shape so asto have dimensions substantially equal to those of the first electrode20, and opposes the whole first surface 21 a. As the porous membranes 24a and 24 b, for example, a nonwoven fabric, cloth or a porous membranewhich is formed by a sol-gel method can be used, and various materialsmay be used for the porous membranes. Of these porous membranes, apolymer membrane containing a fluorine atom or a chlorine atom in itsmain chain, glass cloth or a membrane including irregular continuouspores and containing inorganic oxide, is especially chemically stableand preferable. If an inorganic oxide film having irregular pores isused as the porous membranes 24 a and 24 b, they can also function asdiaphragms. The porous membranes 24 and 27 may be multilayer films of aplurality of porous membranes having different pore-diameters.

The diaphragm 26 a is formed in, for example, a rectangular shape so asto have dimensions substantially similar to those of the first electrode20, and opposes the first surface 22 a of the first electrode 20. Theporous membrane 24 a is interposed between the first surface 22 a of thefirst electrode 20 and the diaphragm 26 a, and adheres tightly to thefirst electrode 20 and the diaphragm 26 a.

The diaphragm 26 b is formed in, for example, a rectangular shape so asto have dimensions substantially equal to those of the second electrode22, and opposes the first surface 23 a of the second electrode 22. Theporous membrane 24 b is interposed between the first surface 23 a of thesecond electrode 22 and the diaphragm 26 b, and adheres tightly to thesecond electrode 22 and the diaphragm 26 b.

The diaphragms 26 a and 26 b are films which allow ions and/or liquid topass therethrough. For the diaphragm 26, various electrolyte membranesand porous membranes having nanopores may be used.

In the sixth embodiment having the above-described structure, effectssimilar to those of the first embodiment can be obtained. It is possibleto obtain a long-life, high-reaction-efficiency electrode unit andelectrolytic device.

Next, various examples and comparative example will be described.

Example 1

For the electrode matrix 21, a flat titanium plate having a thickness(T1) of 0.5 mm is employed. This titanium plate is etched as shown inFIG. 4. In this manner, an electrode is manufactured. In this electrode,a thickness T2 of a region including the smaller-dimension first pores40 (depth of the first pores) is 0.15 mm, and a thickness T3 of a regionincluding the larger-dimension second pores 42 (depth of the secondpores) is 0.35 mm. The first pores 40 have a square shape whose verticesare rounded, and one side R1 of the square obtained by extrapolating thestraight line part is 0.57 mm. The second pores 42 have a square shape,and one side R2 thereof is 2 mm. A width W1 of a linear portion formedbetween adjacent first pores 40 is 0.1 mm and a width W2 of a widelinear portion formed between adjacent second pores 42 is 1.0 mm.

The electrode matrix 21 is processed in advance in a 10-wt % oxalic acidaqueous solution at 80° C. for an hour. 1-butanol is added to iridiumchloride (IrCl₃.nH₂O) to be adjusted to 0.25M (Ir) and the mixture isapplied to the surface (first surface) of the electrode matrix 21 inwhich the first pores 40 are formed, followed by drying and burning. Inthis case, drying is performed at 80° C. for 10 minutes, and the burningis performed at 450° C. for 10 minutes. The above-described application,drying and burning are repeated five times. The electrode matrix madethrough this process is cut out such that the reactive electrode areacan be 3 cm×4 cm. In this manner, the first electrode (anode) 20 ismanufactured. The average coarseness of the flat portion of the firstelectrode 20 except for the recess portions is measured by AFM to be 1μm.

Further, the second electrode (a counterelectrode, a cathode) 22 isproduced by sputtering platinum onto the first surface of the electrodematrix in which the first pores are formed.

The electrode unit 12 shown in FIG. 11 is manufactured, using the firstand second electrodes thus obtained. For the diaphragm 26 a, ananion-exchange membrane, A201 of Tokuyama, Inc is employed, and for thediaphragm 26 b, NAFION (trademark) 117 is employed. A glass cloth(75-μm-thick) is used for the porous membranes 24 a and 24 b. As theholder 25 which holds the electrolyte, porous polystyrene having athickness of 5 mm is provided in the intermediate chamber (electrolytechamber) 19. The first and second electrodes, the porous membrane, thedividing wall and porous polystyrene are put and fixed together usingsilicone seal adhesive and a screw, to form the electrode unit 12. Usingthis electrode unit 12, the electrode unit 12 and the electrolyte device10 shown in FIG. 10 are manufactured.

The anode chamber 16 and the cathode chamber 18 of the electrolytic cell11 are each formed from a vinyl-chloride container in which a straightpathway is formed. The control device 36, the power supply 30, thevoltmeter 34 and the ammeter 32 are provided. A pipe and a pump forsupplying water to the anode and cathode chambers 16 and 18 areconnected to the electrolytic cell 11. Further, a saturated salt watertank, a pipe and a pump for circulating a saturated salt water to theholder (porous polystyrene) 25 of the electrode unit 12 are connected tothe electrode unit. The electrolytic device 10 is operated forelectrolysis at a voltage of 5V and a current of 1.5 A. Aqueoushypochlorous acid is produced on the anode 20 side, and aqueous sodiumhydroxide is produced on the cathode 22 side. Even after continuousoperation for 1000 hours, no substantial rise in voltage or change inproduct concentration is observed. Thus, a stable electrolytic treatmentcan be carried out.

Example 2

With a different mask used in the etching, a first electrode 20 ismanufactured from an electrode matrix of 3×4 cm, having a centralportion of 1×1.4 cm, where first pores 40 each having a square shapewhose one side R1 has a length of 0.7 mm are formed and a width W1 of alinear portion is 0.2 mm. The second pores 42 have a square shape whoseone side has a length of 2 mm. The second pore formed in the centralportion included the first pores in an arrangement of 2×2. The otherstructures are the same as those of Example 1. On these conditions, theelectrode unit 12 and the electrolytic device 10 are manufactured.

The electrolytic device 10 is operated for electrolysis at a voltage of4.8 V and a current of 1.5 A. Aqueous hypochlorous acid is produced onthe anode 20 side, and aqueous sodium hydroxide is produced on thecathode 22 side. Even after continuous operation for 1000 hours, nosubstantial rise in voltage or change in product concentration isobserved. Thus, a stable electrolytic treatment can be carried out.

Example 3

As the porous membrane, a nonwoven fabric made from polyvinylidenechloride is used instead of the glass cloth. The other structures arethe same as those of Example 1. On these conditions, the electrode unit12 and the electrolytic device 10 are manufactured.

The electrolytic device 10 is operated for electrolysis at a voltage of5.1 V and a current of 1.5 A. Aqueous hypochlorous acid is produced onthe anode 20 side, and aqueous sodium hydroxide is produced on thecathode 22 side. Even after continuous operation for 1000 hours, nosubstantial rise in voltage or change in product concentration isobserved. Thus, a stable electrolytic treatment can be carried out.

Example 4

As the porous membrane, a porous titanium oxide membrane includingirregular pores is used instead of the glass cloth. The other structuresare the same as those of Example 1. On these conditions, the electrodeunit 12 and the electrolytic device 10 are manufactured.

The electrolytic device 10 is operated for electrolysis at a voltage of5.2 V and a current of 1.5 A. Aqueous hypochlorous acid is produced onthe anode 20 side, and aqueous sodium hydroxide is produced on thecathode 22 side. Even after continuous operation for 1000 hours, nosubstantial rise in voltage or change in product concentration isobserved. Thus, a stable electrolytic treatment can be carried out.

Example 5

As the porous membrane, a nonwoven fabric made from Teflon is usedinstead of the glass cloth. The other structures are the same as thoseof Example 1. On these conditions, the electrode unit 12 and theelectrolytic device 10 are manufactured.

The electrolytic device 10 is operated for electrolysis at a voltage of5.0 V and a current of 1.5 A. Aqueous hypochlorous acid is produced onthe anode 20 side, and aqueous sodium hydroxide is produced on thecathode 22 side. Even after continuous operation for 1000 hours, nosubstantial rise in voltage or change in product concentration isobserved. Thus, a stable electrolytic treatment can be carried out.

Example 6

A first electrode 20 is manufactured as in Example 1 andelectric-insulating polyvinyl chloride is applied selectively on a widelinear portion (having a width of W2) to form an insulating film byscreen printing. The other structures are the same as those ofExample 1. On these conditions, the electrode unit 12 and theelectrolytic device 10 are manufactured.

The electrolytic device 10 is operated for electrolysis at a voltage of5.3 V and a current of 1.5 A. Aqueous hypochlorous acid is produced onthe anode 20 side, and aqueous sodium hydroxide is produced on thecathode 22 side. Even after continuous operation for 1000 hours, nosubstantial rise in voltage or change in product concentration isobserved. Thus, a stable electrolytic treatment can be carried out.

Example 7

A second electrode (counterelectrode) 22 of a porous structure ismanufactured as in Example 1. As the diaphragm 26, a porous glass film(50-μm-thick) is employed. As the porous membrane 24, a glass cloth(75-μm-thick) is employed. They are then put together using a siliconesealing material and screws to form an electrode unit 12.

Using the electrode unit 12, a one-chamber electrolytic cell 11 and anelectrolyte device 10 shown in FIG. 9 are manufactured. A control device36, a power supply 30, a voltmeter 34 and an ammeter 32 are provided. Apipe and a pump for supplying salt water to an electrolytic chamber 17are provided. The electrolytic device 10 is operated for electrolysis ata voltage of 4.3 V and a current of 1.5 A to produce aqueoushypochlorous acid. Even after continuous operation for 1000 hours, nosubstantial rise in voltage or change in product concentration isobserved. Thus, a stable electrolytic treatment can be carried out.

Example 8

As the porous membrane, a polyphenylene sulfide porous membrane coatedwith a film containing titanium oxide is employed instead of the glasscloth. The polyphenylene sulfide porous membrane coated with a filmcontaining titanium oxide is used to also serve as the diaphragms 26 aand 26 b. The other structures are the same as those of Example 1. Onthese conditions, the electrode unit 12 and the electrolytic device 10are manufactured.

The electrolytic device 10 is operated for electrolysis at a voltage of4.8 V and a current of 1.5 A. Aqueous hypochlorous acid is produced onthe anode 20 side, and aqueous sodium hydroxide is produced on thecathode 22 side. Even after continuous operation for 2000 hours, nosubstantial rise in voltage or change in product concentration isobserved. Thus, a stable electrolytic treatment can be carried out.

Example 9

As the porous membrane, a glass-made nonwoven fabric (filter paper)coated with a film containing titanium oxide is employed instead of thepolyphenylene sulfide porous membrane coated with a film containingtitanium oxide. The other structures are the same as those of Example 8.On these conditions, the electrode unit 12 and the electrolytic device10 are manufactured.

The electrolytic device 10 is operated for electrolysis at a voltage of4.7 V and a current of 1.5 A. Aqueous hypochlorous acid is produced onthe anode 20 side, and aqueous sodium hydroxide is produced on thecathode 22 side. Even after continuous operation for 2000 hours, nosubstantial rise in voltage or change in product concentration isobserved. Thus, a stable electrolytic treatment can be carried out.

Example 10

As the porous membrane, a glass-made nonwoven fabric (filter paper)coated with a film containing zirconium oxide is employed instead of thepolyphenylene sulfide porous membrane coated with a film containingtitanium oxide. The other structures are the same as those of Example 8.On these conditions, the electrode unit 12 and the electrolytic device10 are manufactured.

The electrolytic device 10 is operated for electrolysis at a voltage of4.8 V and a current of 1.5 A. Aqueous hypochlorous acid is produced onthe anode 20 side, and aqueous sodium hydroxide is produced on thecathode 22 side. Even after continuous operation for 2000 hours, nosubstantial rise in voltage or change in product concentration isobserved. Thus, a stable electrolytic treatment can be carried out.

Example 11

As the porous membrane, a membrane further coated with a more precisefilm containing zirconium oxide on an electrode-side surface of theporous membrane is employed instead of the polyphenylene sulfide porousmembrane coated with a film containing titanium oxide. The otherstructures are the same as those of Example 8. On these conditions, theelectrode unit 12 and the electrolytic device 10 are manufactured.

This electrolytic device 10 is operated for electrolysis at a voltage of4.9 V and a current of 1.5 A. Aqueous hypochlorous acid is produced onthe anode 20 side, and aqueous sodium hydroxide is produced on thecathode 22 side. Even after continuous operation for 2000 hours, nosubstantial rise in voltage or change in product concentration isobserved. Thus, a stable electrolytic treatment can be carried out.

Example 12

As the porous membrane, a membrane coated with a Teflon porous membranefurther coated with a film containing zirconium oxide is employedinstead of the polyphenylene sulfide porous membrane coated with a filmcontaining titanium oxide. The other structures are the same as those ofExample 8. On these conditions, the electrode unit 12 and theelectrolytic device 10 are manufactured.

This electrolytic device 10 is operated for electrolysis at a voltage of4.9 V and a current of 1.5 A. Aqueous hypochlorous acid is produced onthe anode 20 side, and aqueous sodium hydroxide is produced on thecathode 22 side. Even after continuous operation for 2000 hours, nosubstantial rise in voltage or change in product concentration isobserved. Thus, a stable electrolytic treatment can be carried out.

Example 13

For the electrode matrix 21, a flat titanium plate having a thickness T1of 0.5 mm is employed. This titanium plate is etched as shown in FIG. 4to manufacture an electrode. In this electrode, a thickness T2 of aregion including the smaller-dimension first pores 40 (depth of thefirst pores) is 0.15 mm, and a thickness T3 of a region including thelarger-dimension second pores 42 (depth of the second pores) is 0.35 mm.The first pores 40 have a rhomboid shape whose long diagonal is 0.69 mmand short diagonal is 0.4 mm. The second pores 42 have a rhomboid shapewhose long diagonal line has a length of 6.1 mm and short diagonal linehas a length of 3.5 mm. A width W1 of a linear portion formed betweenadjacent first pores 40 is 0.15 mm and a width W2 of a wide linearportion formed between adjacent second pores 42 is 1 mm. The otherstructures are the same as those of Example 1. On these conditions, theelectrode unit 12 and the electrolytic device 10 are manufactured.

This electrolytic device 10 is operated for electrolysis at a voltage of5.3 V and a current of 1.5 A. Aqueous hypochlorous acid is produced onthe anode 20 side, and aqueous sodium hydroxide is produced on thecathode 22 side. Even after continuous operation for 1000 hours, nosubstantial rise in voltage or change in product concentration isobserved. Thus, a stable electrolytic treatment can be carried out.

Example 14

For the electrode matrix 21, a flat titanium plate having a thickness T1of 0.5 mm is employed. This titanium plate is etched as shown in FIG. 4to manufacture an electrode. In this electrode, a thickness T2 of aregion including the smaller-dimension first pores 40 (depth of thefirst pores) is 0.15 mm, and a thickness T3 of a region including thelarger-dimension second pores 42 (depth of the second pores) is 0.35 mm.The first pores 40 have a square shape whose one side R1 has a length of0.57 mm. The second pores 42 have a rectangular shape whose long sidehas a length of 40 mm and short side has a length of 4 mm. A width W1 ofa linear portion formed between adjacent first pores 40 is 0.1 mm and awidth W2 of a wide linear portion formed between adjacent second pores42 is 1.0 rum. The other structures are the same as those of Example 1.On these conditions, the electrode unit 12 and the electrolytic device10 are manufactured.

This electrolytic device 10 is operated for electrolysis at a voltage of5.8 V and a current of 1.5 A. Aqueous hypochlorous acid is produced onthe anode 20 side, and aqueous sodium hydroxide is produced on thecathode 22 side. Even after continuous operation for 1000 hours, nosubstantial rise in voltage or change in product concentration isobserved. Thus, a stable electrolytic treatment can be carried out.

Comparative Example 1

An electrolytic device is manufactured in a similar manner to that ofExample 1 except that the continuous porous membrane is not employed inthis example. This electrolytic device is operated for electrolysis at avoltage of 5 V and a current of 1.5 A. Aqueous hypochlorous acid isproduced on the anode side, and aqueous sodium hydroxide is produced onthe cathode side. After continuous operation for 1000 hours, asignificant rise in voltage and a decrease in product concentration areobserved. Thus, this device did not exhibit a long-term stability.

Comparative Example 2

An electrolytic device is manufactured by forming through-holes having adiameter of 1 mm in an electrode matrix by punching to have the sameopening ratio as that of the electrode of Example 1. The otherstructures are the same as those of Example 1. On these conditions, theelectrode unit and the electrolytic device are manufactured.

This electrolytic device is operated for electrolysis at a voltage of5.2 V and a current of 1.5 A. Aqueous hypochlorous acid is produced onthe anode side, and aqueous sodium hydroxide is produced on the cathodeside. After continuous operation for 1000 hours, a significant rise involtage and a decrease in product concentration are observed. Thus, thisdevice did not exhibit a long-term stability.

The present invention is not limited to the embodiments andmodifications described above but the constituent elements of theinvention can be modified in various manners without departing from thespirit and scope of the invention. Various aspects of the invention canalso be extracted from any appropriate combination of a plurality ofconstituent elements disclosed in the embodiments. For example, someconstituent elements may be deleted in all of the constituent elementsdisclosed in the embodiments. Further, the constituent elementsdescribed in different embodiments may be combined arbitrarily.

For example, the first electrode and the second electrode are notlimited to rectangular shapes, but various other forms may be selected.The first and second pores of the first electrode are not limited tosquare shapes, and may have various other shapes such as a rectangular,rhomboid, circular or elliptical shape. Further, the material of eachstructural component is not limited to that employed in the embodimentsor examples discussed, but various other materials may be selected asneeded. The electrolytic cell of the electrode device is not limited toa three-chamber type, but it may as well be applied to a two-chamber- orsingle-chamber type or any electrolytic cells with electrodes ingeneral. The electrolytes and product are not limited to salt orhypochlorous acid, but may be developed into various electrolytes andproducts.

1: An electrode unit comprising: a first electrode including: a firstsurface, a second surface located on an opposite side to the firstsurface, a plurality of first pores opened in the first surface, aplurality of second pores opened in the second surface and having anopening area greater than that of the first pores, a plurality of thefirst pores communicating with a respective one of the second pores; asecond electrode opposing the first surface of the first electrode; anda continuous porous membrane arranged between the first electrode andthe second electrode, so as to cover the first surface of the firstelectrode. 2: The electrode unit of claim 1, wherein an opening area ofthe first pores opened in the first surface is 0.01 to 4 mm². 3: Theelectrode unit of claim 1, wherein an opening area of the second poresopened in the second surface is 1 to 1600 mm². 4: The electrode unit ofclaim 1, wherein a number density of the first pores per unit area ishigher than that of the second pores per unit area. 5: The electrodeunit of claim 1, wherein a catalytic layer is formed on the firstsurface and the second surface of the electrode, and an amount of thecatalytic layer per unit area differs from the first surface to thesecond surface. 6: The electrode unit of claim 1, wherein the firstpores are formed to have a tapered surface or a curved surface whichwidens towards the first surface. 7: The electrode unit of claim 1,wherein the first electrode includes recess portions formed in the firstsurface, and the first surface is formed flat except for the first poresand the recess portions. 8: The electrode unit of claim 7, wherein anaverage surface roughness of a flat portion of the first electrode is10% or less of an average thickness of the porous membrane. 9: Theelectrode unit of claim 1, wherein an opening ratio of first poreslocated in a central portion of the first electrode is less than anopening ratio of first pores located in a peripheral portion of thefirst electrode. 10: The electrode unit of claim 1, further comprising:an electrically insulating film which inhibits liquid from passingtherethrough and is provided on at least a portion of the first surfaceof the first electrode. 11: The electrode unit of claim 1, wherein thesecond electrode has a porous structure including a plurality ofthrough-holes. 12: The electrode unit of claim 1, wherein the porousmembrane is a polymer membrane containing a fluorine atom or a chlorineatom in a main chain thereof. 13: The electrode unit of claim 1, whereinthe porous membrane is a glass cloth. 14: The electrode unit of claim 1,wherein the porous membrane is a membrane including in-planerly orthree-dimensionally irregular pores and containing inorganic oxide. 15:The electrode unit of claim 1, wherein the porous membrane is amulti-layer film in which a plurality of porous films having differentpore diameters are stacked one on another. 16: The electrode unit ofclaim 1, further comprising: a diaphragm provided between the firstsurface of the first electrode and the second electrode, which allows atleast one of ion and liquid to pass therethrough, and wherein the porousmembrane is interposed between the first surface of the first electrodeand the diaphragm. 17: The electrode unit of claim 1, furthercomprising: two diaphragms provided between the first electrode and thesecond electrode so as to oppose each other; and an electrolyte holdingstructure located between the two diaphragms to hold electrolyte. 18: Anelectrolytic cell comprising: an electrolytic chamber and an electrodeunit of claim 1, provided in the electrolytic chamber. 19: Anelectrolytic device comprising: an electrolytic cell including anelectrolytic chamber; an electrode unit of claim 1, provided in theelectrolytic chamber; and a power supply which applies a voltage to thefirst electrode and the second electrode of the electrode unit. 20: Theelectrolytic device of claim 19, wherein an electrolyte containingchloride ions is electrolyzed by the electrode unit.